Focus ring for semiconductor treatment and plasma treatment device

ABSTRACT

A focus ring for a plasma processing apparatus has an inner region, middle region, and outer region, disposed in this order from the inner side to surround a target substrate. On the side to be exposed to plasma, the surfaces of the inner region and outer region consist essentially of a dielectric, while the surface of the middle region consists essentially of a conductor. The middle region is arranged to shift the peak of plasma density to the outside of the peripheral edge of the target substrate. If there is no middle region, the peak of plasma density appears substantially directly above the peripheral edge of the target substrate.

TECHNICAL FIELD

The present invention relates to a focus ring and plasma processingapparatus for a semiconductor process, and more particularly to a focusring and plasma processing apparatus that prevent abnormal electricdischarge from occurring on the peripheral portion of a targetsubstrate, such as a wafer, during a plasma process. The term“semiconductor process” used herein includes various kinds of processeswhich are performed to manufacture a semiconductor device or a structurehaving wiring layers, electrodes, and the like to be connected to asemiconductor device, on a target substrate, such as a semiconductorwafer or an LCD substrate, by forming semiconductor layers, insulatinglayers, and conductive layers in predetermined patterns on the targetsubstrate.

BACKGROUND ART

FIG. 8 is a schematic view showing the general structure of a plasmaetching apparatus. The plasma etching apparatus has an airtight andcylindrical process chamber 50. A worktable (used also as a lowerelectrode) 51 for supporting a wafer W handled as a target substrate isdisposed (e.g. movable up and down) on the lower side in the processchamber 50. A showerhead (used also as an upper electrode) 52 forsupplying a process gas is disposed on the upper side in the processchamber 50 and faces the lower electrode 51 in parallel therewith. Thetwo electrodes 51 and 52 are respectively supplied with RF (radiofrequency) powers different in frequency from first and second RF powersupplies 53 and 54 through matching circuits 53A and 54A. With the RFpowers applied to the electrodes 51 and 52, an RF electric field isformed in the process chamber 50. The RF electric field helps theprocess gas turn into plasma, which then etches a film, such as aninsulating film, on the surface of the wafer W.

A focus ring 55 is disposed on the peripheral portion of the lowerelectrode 51 and surrounds the wafer W on the lower electrode 51. On theother hand, a shield ring 56 is disposed on the peripheral portion ofthe upper electrode 52. The focus ring 55 and shield ring 56 work onplasma generated between the upper and lower electrodes 51 and 52 tofocus toward the wafer W.

In the conventional plasma etching apparatus, problems have been foundin that abnormal electric discharge tends to occur on the peripheralportion of a wafer W, and lowers the etching planar uniformity and/orselectivity.

DISCLOSURE OF INVENTION

An object of the present invention is to provide a focus ring and plasmaprocessing apparatus, which prevent abnormal electric discharge fromoccurring during plasma processing on the peripheral portion of a targetsubstrate, such as a wafer.

According to a first aspect of the present invention, there is provideda focus ring to be used in a plasma processing apparatus, which excitesa process gas to turn into plasma in an airtight process chamber andutilizes the plasma to perform a semiconductor process on a targetsubstrate placed on a worktable, wherein the focus ring is placed tosurround the target substrate in order to cause the plasma to focustoward the target substrate, the focus ring comprising:

-   -   an inner region configured to surround the target substrate, and        having a surface consisting essentially of a dielectric on a        side to be exposed to the plasma;    -   a middle region surrounding the inner region, and having a        surface consisting essentially of a conductor on a side to be        exposed to the plasma; and    -   an outer region surrounding the middle region, and having a        surface consisting essentially of a dielectric on a side to be        exposed to the plasma.

According to a second aspect of the present invention, there is provideda plasma processing apparatus for a semiconductor process, comprising:

-   -   an airtight process chamber;    -   a supply system configured to supply a process gas into the        process chamber;    -   an exhaust system configured to vacuum-exhaust the process        chamber;    -   an exciting mechanism configured to excite the process gas to        turn into plasma;    -   a worktable disposed in the process chamber and having a main        mount surface to support a target substrate; and    -   a focus ring according to a first aspect and disposed to        surround the target substrate in order to cause the plasma to        focus toward the target substrate.

According to a third aspect of the present invention, there is provideda focus ring to be used in a plasma processing apparatus, which excitesa process gas to turn into plasma in an airtight process chamber andutilizes the plasma to perform a semiconductor process on a targetsubstrate placed on a worktable, wherein the focus ring is placed tosurround the target substrate in order to cause the plasma to focustoward the target substrate, the focus ring comprising:

-   -   a first region configured to surround the target substrate, and        having a surface consisting essentially of a dielectric on a        side to be exposed to the plasma; and    -   a second region surrounding the first region, and having a        surface consisting essentially of a dielectric on a side to be        exposed to the plasma,    -   wherein the first region has a resistance lower than the second        region in a thickness direction.

According to a fourth aspect of the present invention, there is provideda plasma processing apparatus for a semiconductor process, comprising:

-   -   an airtight process chamber;    -   a supply system configured to supply a process gas into the        process chamber;    -   an exhaust system configured to vacuum-exhaust the process        chamber;    -   an exciting mechanism configured to excite the process gas to        turn into plasma;    -   a worktable disposed in the process chamber and having a main        mount surface to support a target substrate; and    -   a focus ring according to a third aspect and disposed to        surround the target substrate in order to cause the plasma to        focus toward the target substrate.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a structural view showing a plasma etching apparatus, which isa plasma processing apparatus according to an embodiment of the presentinvention;

FIG. 2 is an enlarged sectional view showing the relationship between afocus ring, worktable, and wafer, in the plasma etching apparatus shownin FIG. 1;

FIGS. 3A and 3B are plan views respectively showing the focus ring inFIG. 2 and its modification;

FIGS. 4A, 4B, and 4C are views respectively showing modifications of thefocus ring shown in FIG. 2;

FIG. 5 is an enlarged sectional view showing the relationship between afocus ring, worktable, and wafer, in a plasma etching apparatusaccording to another embodiment of the present invention;

FIG. 6 is a plan view showing the focus ring in FIG. 5;

FIGS. 7A, 7B, and 7C are views respectively showing modifications of thefocus ring shown in FIG. 5;

FIG. 8 is a schematic view showing the general structure of a plasmaetching apparatus; and

FIGS. 9A and 9B are enlarged sectional views each showing therelationship between a conventional focus ring, and a worktable andwafer, in a plasma etching apparatus.

BEST MODE FOR CARRYING OUT THE INVENTION

In the process of developing the present invention, the inventorsstudied the causes as to why abnormal electric discharge tends to occurduring plasma processing on the peripheral portion of a targetsubstrate, such as a wafer. As a result, the inventors have arrived atthe findings given below.

FIGS. 9A and 9B are enlarged sectional views each showing therelationship between a conventional focus ring, and a worktable andwafer, in a plasma etching apparatus. As shown in FIG. 9A, the focusring 55 has a top face almost level with the top surface of the wafer W,on a side to be exposed to plasma. An inner extending step 55 a isformed on the inner peripheral end of the focus ring 55 and extendsunder the wafer W. The focus ring 55 is formed of a dielectric body(insulating body), such as quartz. Accordingly, the plasma is attractedby the wafer W rather than the focus ring 55, so that the plasma isfocused toward the surface of the wafer W, as shown by arrows F1 in FIG.9A.

Since the plasma is focused by the focus ring 55, the plasmaconcentrates near the peripheral edge of the wafer W, as shown by thearrows F1. In other words, as shown by a curved line PD1 in FIG. 9B, theplasma density becomes higher at the periphery of the wafer W than atthe center thereof. Due to such bad uniformity in the plasma density,abnormal electric discharge is likely to occur on the periphery of thewafer W, where the plasma density is higher. This causes problems inthat the etching planar uniformity and/or selectivity become lower.

Embodiments of the present invention achieved on the basis of thefindings given above will now be described with reference to theaccompanying drawings. In the following description, the constituentelements having substantially the same function and arrangement aredenoted by the same reference numerals, and a repetitive descriptionwill be given only when necessary.

FIG. 1 is a structural view showing a plasma etching apparatus, which isa plasma processing apparatus according to an embodiment of the presentinvention. The plasma etching apparatus 1 has an airtight cylindricalprocess chamber 2 for accommodating a target substrate, such as asemiconductor wafer W. The process chamber 2 is formed of a conductivebody, such as aluminum with an anodized inner surface, and is groundedthrough a ground line. A vacuum exhaust section VE including a turbomolecular pump and so forth is connected to a lower portion of thesidewall of the process chamber 2 through an exhaust line. The vacuumexhaust section VE exhausts the process chamber 2, and sets it at apredetermined vacuum level.

On the other hand, a disc like showerhead 4 is disposed on the ceilingof the process chamber 2, and is connected to a process gas supplysection GS of an etching gas and other gases through a gas supply line.The showerhead 4 is provided with a number of holes 4A formed on thebottom face, for spouting process gases. The showerhead 4 has a bottomplate formed of an electrode plate, and is also used as an upperelectrode. The showerhead 4 is electrically insulated from the casing ofthe process chamber 2 by an insulating body 3A. A shield ring 5 isdisposed on the peripheral edge of the electrode plate of the showerhead4.

A worktable 11 formed of a cylindrical column is disposed on the bottomof the process chamber 2 and has a main mount surface 11 a for placing awafer W thereon. The peripheral portion of the worktable 11 has asub-mount surface 11 b positioned lower than the main mount surface 11a, such that a focus ring 12 is placed on the sub-mount surface 11 b tosurround the wafer W. The worktable 11 is formed of a conductive body,such as aluminum with an anodized surface, and is also used as a lowerelectrode. The worktable 11 is disposed in an insulating frame 6. Theworktable 11 is also electrically insulated from the casing of theprocess chamber 2 by an insulating plate 3B made of, e.g., ceramic.

An electrostatic chuck 15 having a diameter almost the same as the waferW is disposed on the worktable 11. The electrostatic chuck 15 isarranged such that a conductive layer is sandwiched between two polymerfilms of polyimide. The conductive layer is supplied with a DC voltageof, e.g., 1.5 kV from a DC high power supply 16 disposed outside theprocess chamber 2. As a consequence, a wafer W placed on theelectrostatic chuck 15 is attracted and held on the top on the worktable11 by means of Coulomb's force.

The upper electrode of the showerhead 4 is connected to an RF (radiofrequency) power supply 9 through a matching circuit 8. The upperelectrode 4 is supplied with an RF power of 13.56 MHz, 27.12 MHz, or 60MHz from the RF power supply 9. On the other hand, the lower electrodeor worktable 11 is connected to an RF power supply 14 through a matchingcircuit 13. The lower electrode 11 is supplied with an RF power of 800kHz or 2 MHz from the RF power supply 14. The RF power applied to theupper electrode 4 forms an RF electric field in the process chamber 2,for exciting a process gas to turn into plasma. The RF power applied tothe lower electrode 11 generates a self-bias in the worktable 11, forattracting ions towards the wafer W.

FIG. 2 is an enlarged sectional view showing the relationship betweenthe focus ring 12, worktable 11, and wafer W, in the plasma etchingapparatus 1. FIG. 3A is a plan view showing the focus ring 12. As shownin FIG. 3A, the focus ring 12 has an inner region 12 a, middle region 12b, and outer region 12 c disposed in this order from the inner side tosurround the wafer W. An inner extending step 12 d is formed on theinner side of the inner region 12 a and extends under the wafer W. Theinner region 12 a, middle region 12 b, outer region 12 c, and innerextending step 12 d are arranged concentric. On the side (upper side) tobe exposed to plasma, the surfaces of the inner region 12 a, outerregion 12 c, and inner extending step 12 d are formed of a dielectricbody, while the surface of the middle region 12 b is substantiallyformed of a conductive body (including a case where a thin protectioninsulating film is formed on the outermost surface). The surface of themiddle region 12 b is formed of a number of surface portions disposedequidistantly in the angular direction.

The middle region 12 b is arranged to shift the peak of plasma densityto the outside of the peripheral edge of the wafer W. If there is nomiddle region 12 b, the peak of plasma density appears substantiallydirectly above the peripheral edge of the wafer W (see the curved linePD1 in FIG. 9B). More specifically, the width of the inner region 12 ain the radial direction is set to be 0 to 5 mm, and preferably 1 to 3mm. The width of the middle region 12 b in the radial direction is setto be 1 to 10 mm, and preferably 2 to 5 mm. The ratio of the width ofthe inner region 12 a and outer region 12 c in the radial directionrelative to the width of the middle region 12 b in the radial directionis set to be 2 to 29, and preferably 5 to 14.

The focus ring 12 has a ring-like main body 17 formed of a dielectricbody, such as quartz, or ceramic, e.g., Al₂O₃ or SiC. The main body 17is provided with a number of throughholes 17 a formed equidistantly inthe angular direction, at positions displaced toward the inside in theradial direction. Adjustment members 18 formed of a conductive body,such as silicon or aluminum surfaced with alumina, are inserted into thethroughholes 17 a. The inner region 12 a, outer region 12 c, and innerextending step 12 d employ the main body 17, while the middle region 12b employs the adjustment members 18.

Each of the adjustment members 18 has a stem inserted in thecorresponding throughhole 17 a and a flange 18 a connected at itsbottom. The sub-mount surface 11 b of the worktable 11 to place thefocus ring 12 thereon is provided with recesses 11 c formed atpredetermined intervals in the angular direction, for respectivelyaccepting the flanges 18 a. The focus ring 12 is positioned relative tothe worktable 11 by means of engagement between the flanges 18 a andrecesses 11 c. The depth of the recesses 11 c is set in accordance withthe thickness of the flanges 18 a. The recesses 11 c may be formed ofcounterbores or the like the same as those used for screws for fixingthe worktable 11.

The conductive adjustment members 18 inserted in the throughholes 17 aof the main body 17 work as antennas for attracting plasma. Since theadjustment members 18 are exposed on the surface and in contact withplasma, the plasma is attracted onto the adjustment members 18. In otherwords, the focus ring 12 works on the plasma to focus it toward thewafer W as a whole, but the adjustment members 18 attracts part of thefocusing plasma. As a consequence, as shown by a curved line PD2 in FIG.2, the peak of plasma density is shifted toward the adjustment members18 and is modified to be higher at the shifted position, as compared tothe peak of plasma density appearing substantially directly above theperipheral edge of the wafer W (see the curved line PD1 in FIG. 9B)where there are no adjustment members 18. It follows that the plasmadensity becomes uniform over the central potion and the peripheral edgeof the wafer W, so that abnormal electric discharge is reliablyprevented from occurring on the peripheral edge of the wafer W.

Next, an explanation will be given of a processing method performed inthe plasma etching apparatus 1 shown in FIG. 1. Specifically, theprocess chamber 2 is supplied with a process gas while it is exhausted,so that the inside of the process chamber 2 is kept at a predeterminedvacuum level. In this state, the worktable (lower electrode) 11 issupplied with an RF power of 2 MHz, and the showerhead (upper electrode)4 is supplied with an RF power of 60 MHz. As a consequence, plasma ofthe process gas is generated between the worktable 11 and showerhead 4.The plasma is focused toward the surface of the wafer W by the agency ofthe focus ring 12, and etches the wafer W.

At this time, as shown by the curved line PD2 in FIG. 2, a high peak ofthe plasma density appears outside the peripheral edge of the wafer W,due to the middle region 12 b of the focus ring 12, which corresponds tothe adjustment members 18 and thus is substantially conductive. As aconsequence, the plasma density becomes uniform over the central potionand the peripheral edge of the wafer W, so that abnormal electricdischarge is reliably prevented from occurring on the peripheral edge ofthe wafer W.

FIG. 4A is a view showing a modification 12X of the focus ring 12. Thefocus ring 12X differs from the focus ring 12 shown in FIG. 2, in thatit employs adjustment members 18X respectively formed of stems with noflanges. Specifically, a ring-like main body 17 formed of a dielectricbody, such as quartz, is provided with a number of throughholes 17 aformed equidistantly in the angular direction. The adjustment members18X formed of a conductive body are inserted into the throughholes 17 a.Since the adjustment members 18X have no flanges 18 a, there is no needfor the sub-mount surface 11 b of the worktable 11 to have the recesses11 c.

FIG. 4B is a view showing another modification 12Y of the focus ring 12.The focus ring 12Y differs from the focus ring 12 shown in FIG. 2, inthat it employs adjustment members 18Y formed of circular plates with nostems. Specifically, a ring-like main body 17 formed of a dielectricbody, such as quartz, is provided with a number of throughholes 17 aformed equidistantly in the angular direction. The circular plateadjustment members 18Y are disposed along the bottom of the throughholes17 a. The sub-mount surface 11 b of the worktable 11 may be providedwith a ring-like recess.

FIG. 4C is a view showing still another modification 12Z of the focusring 12. FIG. 3B is a plan view showing the focus ring 12Z. The focusring 12Z differs from the focus ring 12 shown in FIG. 2, in that itemploys a ring-like adjustment member 18Z formed of a substantiallyconductive body. Specifically, a ring-like main body 17Z formed of adielectric body, such as quartz, is provided with a ring-like groove17Za formed in the upper surface of the main body 17Z and notpenetrating through the main body 17Z in the thickness direction. Thering-like adjustment member 18Z formed of a conductive body is disposedin the groove 17Za. As a consequence, a continuous ring-like surface,which is substantially conductive, is formed in the middle region 12 b,as shown in FIG. 3B.

FIG. 5 is an enlarged sectional view showing the relationship betweenthe focus ring 22, worktable 11, and wafer W, in a plasma etchingapparatus 20 according to another embodiment of the present invention.The plasma etching apparatus 20 has a structure the same as the plasmaetching apparatus 1 shown in FIG. 1, except some portions relating to afocus ring 22.

FIG. 6 is a plan view showing the focus ring 22. As shown in FIG. 6, thefocus ring 22 has an inner region 22 a, middle region 22 b, and outerregion 22 c disposed in this order from the inner side to surround thewafer W. An inner extending step 22 d is formed on the inner side of theinner region 22 a and extends under the wafer W. The inner region 22 a,middle region 22 b, outer region 22 c, and inner extending step 22 d arearranged concentric. On the side (upper side) to be exposed to plasma,the surfaces of the inner region 22 a, outer region 22 c, middle region22 b, and inner extending step 22 d are formed of a dielectric body. Inthe following explanation, the inner region 22 a and middle region 22 bare referred to as a first region, and the outer region 22 c is referredto as a second region, when necessary.

The first region 22 a and 22 b is arranged such that it has a resistancelower than the second region 22 c in the thickness direction, and thepeak of plasma density appearing substantially directly above theperipheral edge of the wafer W (see the curved line PD1 in FIG. 9B)becomes lower than that in a case where the first region 22 a and 22 bhas a resistance equal to that of the second region 22 c in thethickness direction. In other words, the focus ring 22 is designed suchthat the first region 22 a and 22 b has an insulating level lower thanthe second region 22 c. More specifically, the width of the inner region22 a in the radial direction is set to be 0 to 5 mm, and preferably 1 to3 mm. The width of the middle region 22 b in the radial direction is setto be 5 to 15 mm, and preferably 8 to 12 mm. The ratio of the width ofthe second region 22 c in the radial direction relative to the width ofthe first region 22 a and 22 b in the radial direction is set to be 0.5to 5, and preferably 1 to 2.3.

The focus ring 22 has a ring-like main body 27 formed of a dielectricbody, such as quartz, or ceramic, e.g., Al₂O₃ or SiC. The main body 27is provided with a ring-like groove 27 a formed in the lower surface ofthe main body 27 and not penetrating through the main body 27 in thethickness direction, at a position displaced toward the inside in theradial direction. An adjustment member 28 formed of a conductive body,such as silicon or aluminum surfaced with alumina, is disposed in thegroove 27 a. The inner region 22 a, outer region 22 c, and innerextending step 22 d are formed only of the main body 27, while themiddle region 22 b is formed of the combination of the main body 27 withthe adjustment member 28.

Since the conductive adjustment member 28 is disposed in the groove 27 aof the main body 27, the first region 22 a and 22 b has a resistancelower than the second region 22 c in the thickness direction.Accordingly, the function of the focus ring 22 to repel plasma (i.e.,the function of directing plasma toward the wafer W) is lower at thefirst region 22 a and 22 b. This suppresses the plasma focusing towardthe wafer W, so that the plasma is prevented from excessivelyconcentrating on the peripheral edge of the wafer W. As a consequence,the peak of plasma density appearing substantially directly above theperipheral edge of the wafer W (see the curved line PD1 in FIG. 9B)becomes lower, as shown by a curved line PD3 in FIG. 5. It follows thatthe difference in plasma density between the central potion and theperipheral edge of the wafer W becomes smaller, so that abnormalelectric discharge is reliably prevented from occurring on theperipheral edge of the wafer W.

Next, an explanation will be given of a processing method performed inthe plasma etching apparatus 20 shown in FIG. 5. The explanation will begiven with reference to FIG. 1 as well as FIG. 5, because the membersnot shown in FIG. 5 are common to FIG. 1. Specifically, the processchamber 2 is supplied with a process gas while it is exhausted, so thatthe inside of the process chamber 2 is kept at a predetermined vacuumlevel. In this state, the worktable (lower electrode) 11 is suppliedwith an RF power of 2 MHz, and the showerhead (upper electrode) 4 issupplied with an RF power of 60 MHz. As a consequence, plasma of theprocess gas is generated between the worktable 11 and showerhead 4. Theplasma is focused toward the surface of the wafer W by the agency of thefocus ring 12, and etches the wafer W.

At this time, as shown by the curved line PD3 in FIG. 5, a very low peakof the plasma density appears substantially directly above theperipheral edge of the wafer W, due to the first region 22 a and 22 b ofthe focus ring 12 having a lower insulating level, which corresponds tothe adjustment member 28. As a consequence, the difference in plasmadensity between the central potion and the peripheral edge of the waferW becomes smaller, so that abnormal electric discharge is reliablyprevented from occurring on the peripheral edge of the wafer W.

FIG. 7A is a view showing a modification 22X of the focus ring 22. Thefocus ring 22X differs from the focus ring 22 shown in FIG. 5, in thatthe top surface of a dielectric main body 27X is inclined outwardlyupward. With this arrangement, the thickness of the dielectric main body27X itself is smaller at the position closer to the inner side in theradial direction, and thus a first region 22 a and 22 b has a lowerinsulating level. As a consequence, the peak of the plasma densityappearing substantially directly above the peripheral edge of the waferW is further lower.

FIG. 7B is a view showing another modification 22Y of the focus ring 22.The focus ring 22Y differs from the focus ring 22 shown in FIG. 5, inthat the top surface of a conductive adjustment member 28Y is inclinedoutwardly downward. With this arrangement, the thickness of theconductive adjustment member 28Y itself is larger at the position closerto the inner side in the radial direction, and thus a first region 22 aand 22 b has a lower insulating level. As a consequence, the peak of theplasma density appearing substantially directly above the peripheraledge of the wafer W is further lower.

FIG. 7C is a view showing a modification 22Z of the focus ring 22. Thefocus ring 22Z differs from the focus ring 22 shown in FIG. 5, in thatit is formed only of a dielectric main body 27Z without the adjustmentmember 28. The dielectric main body 27Z has three portions different inthickness, such that the thickness is smaller at the position closer tothe inner side in the radial direction. The innermost portion is aninner extending step 22 d, the middle portion corresponds to a firstregion 22 a and 22 b, and the outer portion corresponds to a secondregion 22 c. With this arrangement, the first region 22 a and 22 b has aresistance lower than the second region 22 c in the radial direction,resulting in the same effect as the focus ring 22 shown in FIG. 5.

A focus ring may be formed by combining the dielectric main body 27Xhaving a top surface inclined outwardly upward shown in FIG. 7A, and theconductive adjustment member 28Y having a top surface inclined outwardlydownward shown in FIG. 7B. Furthermore, where a focus ring is formedonly of a dielectric main body, as shown in FIG. 7C, the main body mayhave a top surface inclined outwardly upward.

In the embodiments described above, silicon or aluminum surfaced withalumina exemplifies a conductive body for the adjustment member of afocus ring. Alternatively, a conductive body, such as silicon carbide orcarbon, compatible with use in a semiconductor process chamber, may beused. In the focus rings shown in FIGS. 2, 4A, and 4B, the performanceof the focus rings may be adjusted by changing the intervals between theadjustment members. In the focus rings shown in FIGS. 5, 7A, and 7B, theconductive adjustment member may be divided into parts disposed atintervals in the angular direction.

In the embodiments described above, an etching apparatus of the parallelplate type is shown as an example, but the present invention may beapplied to a plasma etching apparatus of the magnetron type, RIE type,or ECR type. Furthermore, the present invention may be applied to aplasma film-forming apparatus, such as a plasma CVD apparatus.Furthermore, the present invention may be applied to a target substrateother than a semiconductor wafer, such as an LCD substrate or glasssubstrate.

The present invention is not limited to the above embodiments and can bevariously modified without departing from the spirit and scope of theinvention when practiced. Also, the embodiments can be appropriatelycombined as much as possible when they are practiced. In this case,combined effects are obtained.

1. A plasma processing apparatus for a semiconductor process,comprising: an airtight process chamber; a supply system configured tosupply a process gas into the process chamber; an exhaust systemconfigured to vacuum-exhaust the process chamber; an exciting mechanismconfigured to excite the process gas to turn into plasma; a worktabledisposed in the process chamber and having a main mount surface tosupport a target substrate having a target surface extending in ahorizontal direction; and a focus ring disposed to surround the targetsubstrate in order to cause the plasma to focus toward the targetsurface, wherein the focus ring comprises a ring main body consistingessentially of a material selected from the group consisting of quartz,and ceramic of Al₂O₃ or SiC, and an adjustment member fitted in the ringmain body and consisting essentially of a material selected from thegroup consisting of silicon, aluminum surfaced with alumina, siliconcarbide, and carbon, the ring main body and the adjustment member arepositioned relative to one another and the target surface to set a peakof density of the plasma at a position outside an outer edge of thetarget substrate so as to provide a more uniform density of the plasmaon the target substrate, the ring main body provides an inner regionconfigured to surround the target substrate, and having a surfaceextending substantially in the horizontal direction to surround thetarget substrate and consisting essentially of a dielectric on a side tobe exposed to the plasma, the adjustment member provides a middle regionsurrounding the inner region, and having a surface extendingsubstantially in the horizontal direction to surround the targetsubstrate and consisting essentially of an electric conductor that iscontinuous in a horizontal angular direction on a side to be exposed tothe plasma, and the ring main body also provides an outer regionsurrounding the middle region, and having a surface extendingsubstantially in the horizontal direction to surround the targetsubstrate and consisting essentially of a dielectric on a side to beexposed to the plasma, and wherein the ring main body further includesan inner extending step consisting essentially of a dielectric and beingdisposed on an inner side of the inner region to extend below and spacedapart from the target substrate.
 2. The plasma processing apparatusaccording to claim 1, wherein the inner region has a width of 0 to 5 mmin a radial direction.
 3. The plasma processing apparatus according toclaim 2, wherein the middle region has a width of 1 to 10 mm in a radialdirection.
 4. The plasma processing apparatus focus ring according toclaim 1, wherein the surfaces of the inner region, the middle region,and the outer region are flush with each other.
 5. The plasma processingapparatus according to claim 1, wherein the supply system is configuredto supply as the process gas an etching gas for etching the targetsurface.
 6. A plasma processing apparatus for a semiconductor process,comprising: an airtight process chamber; a supply system configured tosupply a process gas into the process chamber; an exhaust systemconfigured to vacuum-exhaust the process chamber; an exciting mechanismconfigured to excite the process gas to turn into plasma; a worktabledisposed in the process chamber and having a main mount surface tosupport a target substrate having a target surface extending in ahorizontal direction; and a focus ring disposed to surround the targetsubstrate in order to cause the plasma to focus toward the targetsurface, wherein the focus ring comprises a ring main body consistingessentially of a material selected from the group consisting of quartz,and ceramic of Al₂O₂or SiC, and an adjustment member fitted in the ringmain body and consisting essentially of a material selected from thegroup consisting of silicon, aluminum surfaced with alumina, siliconcarbide, and carbon, the ring main body and the adjustment member arepositioned relative to one another and the target surface to suppress anincrease in density of the plasma at an outer edge of the targetsubstrate so as to provide a more uniform density of the plasma on thetarget substrate, the ring main body and the adjustment member arearranged to form a first region configured to surround the targetsubstrate, and a second region surrounding the first region, the firstregion and the second region respectively having a first surface and asecond surface extending substantially in the horizontal direction tosurround the target substrate and consisting essentially of a dielectricprovided by the ring main body on a side to be exposed to the plasma,and the ring main body has a ring-like groove that is continuous in ahorizontal angular direction formed in a lower portion corresponding tothe first region, and the adjustment member has a ring shape that iscontinuous in a horizontal angular direction to surround the targetsubstrate and is fitted in the ring-like groove, such that resistance ofthe first region below the first surface is lower than that of thesecond region below the second surface in a thickness direction, whereinthe ring main body further includes an inner extending step consistingessentially of a dielectric and being disposed on an inner side of thefirst region to extend below and spaced apart from the target substrate.7. The plasma processing apparatus according to claim 6, wherein thering main body is thinner at an inner periphery than at an outerperiphery.
 8. The plasma processing apparatus according to claim 6,wherein the adjustment member is thicker at an inner periphery than atan outer periphery.
 9. The plasma processing apparatus according toclaim 6, wherein the first and second surfaces of the first and secondregions are flush with each other.
 10. The plasma processing apparatusaccording to claim 6, wherein the supply system is configured to supplyas the process gas an etching gas for etching the target surface.